Moreover, leptin-deficient ob/ob mice and leptin receptor-deficient db/db mice were important for their wide use in obesity-induced T2DM (Drel et al., 2006), although leptin or leptin receptor disorder is not a key point in human T2DM (Wang, Chandrasekera & Pippin, 2014). Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.